Project Summary The research project described herein seeks to determine the genetics and cell biological mechanisms that drive depolyploidization of enterocytes to functional intestinal stem cells in the Drosophila intestinal epithelium. New stem cells are commonly thought to arise by symmetric division of existing stem cells. However, Preliminary Data demonstrates that rapid and severe depletion of ISCs during the physiological stress of starvation initiates ploidy reduction (depolyploidization) to replace ISCs upon re-feeding. Our Preliminary Data underline the importance in considering dedifferentiation as a more general mechanism of stem cell replacement in other tissues. Our preliminary data open three compelling questions for future study, which we will endeavor to address with the experiments described in this proposal: What conditional states of the ISC invoke the use of depolyploidization (Specific Aim 1)? What signals initiate fate reversion and depolyploidization (Specific Aim 2)? What cell biology drives depolyploidization and at what frequency is genomic fidelity maintained (Specific Aim 3)? As this is truly an uncharted area of research, we anticipate that the mechanisms delineated in the genetically tractable Drosophila model will provide a foundation for future studies in other tissues and organisms.